Gestational diabetes mellitus constitutes a large majority of patients with diabetes seen during pregnancy. Even though gestational diabetes comprises a major public health problem, its diagnosis, pathophysiology, management and the evaluation of its natural history has not received significant attention. Nevertheless, gestational diabetes results in significant perinatal morbidity in addition to the long term risk to the mother. The overall aim of the proposed studies is to test the hypothesis that gestational diabetes can be detected early in pregnancy in a high risk population and that early intervention will decrease the perinatal morbidity and mortality. A second aim is to test the efficacy of diet and diet plus insulin for the clinical management of gestational diabetes. It is hypothesized that dietary regulation of disturbed metabolism of gestational diabetes will not be able to optimally control metabolism. Other second- ary aims that will evolve from these studies would be to define criteria for glucose intolerance early in pregnancy specifically in relation to perinatal outcome and to evaluate whether characterization of gestationally diabetic women by their insulin response to glucose load can help in classifying these patients in relation to their clinical course and perinatal outcome. Finally, this clinical core protocol will provide and characterize the subject population for other studies in the perinatal Emphasis Research Center (PERC). These studies are important because they have a direct relation to an important clinical problem and would provide the basis for the management of gestational diabetes.